This study was conducted to determine whether nutritional status contributes to the amenorrhea associated with long distance running. Dietary intakes and biochemical measures of nutritional status were compared in highly trained amenorrheic (AM) and eumenorrheic (EU) women runners matched for height, weight, percent fat (11% to 12%) and training distance (113 km/week). Serum estradiol (E2) (EU, 104.7 pg/ml, versus AM, 22.5 pg/ml) and cortisol (EU, 22.4 micrograms/dl, versus AM, 26.6 micrograms/dl) concentrations differed between the two groups. Three-day dietary records revealed that fat intake by AM runners was significantly lower than by EU runners (EU, 97 gm/day, versus AM, 66 gm/day). AM runners consumed large amounts of vitamin A activity, probably in the form of B-carotene, and fairly high quantities of crude fiber. Zinc intake by AM runners was well below the recommended dietary allowances (RDA), compared with EU runners (EU, 15.4 mg, versus AM, 10.9 mg). Further, plasma zinc tended to be lower for the AM runners (EU, 85.7 micrograms/dl, versus AM, 81.2 micrograms/dl). It was concluded that the potential contributions of dietary fat, B-carotene, and zinc to inducing changes in menstrual function and the metabolism of certain hormones should be investigated.